Today, non-aqueous electrolyte secondary batteries are in wide use as secondary batteries with high energy density. In such a non-aqueous electrolyte secondary battery, for example, lithium ions are transferred between a positive electrode and a negative electrode to carry out charge and discharge.
In such a non-aqueous electrolyte secondary battery in general, a composite oxide of lithium transition metals having a layered structure of lithium nickelate (LiNiO2), lithium cobaltate (LiCoO2) or the like is used as the positive electrode, and a carbon material capable of storing and releasing lithium, a lithium metal, a lithium alloy, or the like is used as the negative electrode (see, for example, Patent Document 1).
The use of the non-aqueous electrolyte secondary battery allows a discharge capacity of 150 mAh/g to 180 mAh/g, a potential of about 4 V, and a theoretical capacity of about 260 mAh/g to be obtained.
The non-aqueous electrolyte produced by dissolving an electrolyte salt such as lithium tetrafluoroborate (LiBF4) and lithium hexafluorophosphate (LiPF6) in an organic solvent such as ethylene carbonate and diethyl carbonate is used.
However, such a non-aqueous electrolyte secondary battery with lithium ions is costly.
Therefore, researches on non-aqueous electrolyte secondary batteries using sodium ions supplied in abundance from seawater instead of lithium ions have recently been started. The use of sodium abundant in supply as a resource allows non-aqueous electrolyte secondary batteries to be provided less costly.
Examples of researches on such a non-aqueous electrolyte secondary battery using sodium ions are very limited in number, among which a battery that uses sodium ferrite (NaFeO2) for a positive electrode and sodium perchlorate (NaClO4) as a peroxide for a negative electrode has been proposed (see for example Non-patent Document 1).
[Patent Document 1] JP 2003-151549 A
[Non-patent Document 1] The 45th Battery Symposium, Abstract Volume, pp. 268-269